1. Field of the Invention
The present invention relates generally to a computer implemented method, data processing system, and computer program product for stabilizing port addressing. More specifically, the present invention relates to establishing consistent addressing of a host to a controller contemporaneous with logical unit ownership changes.
2. Description of the Related Art
Architects of modern data processing systems have expanded storage capacity present in hard drives and other storage media. A recent innovation has been the ability to place multiple drives under the control of a common storage controller to form a storage subsystem. Storage subsystems provide an ability to form redundant disk arrays, as well as improve the ability to scale a system as a customer's data processing needs grow.
A storage subsystem is an assembly of at least two storage controllers and at least one logical unit or logical unit number (LUN) coupled to at least one of the storage controllers. A storage controller is a communication device that includes a processor and memory, as well as a port to a network. The network can be a fibre channel based network, or other forms of storage area networks (SAN). Fibre channel is a gigabit speed networking technology primarily used for SAN. Fibre channel may be in any form promulgated by the International Committee for Information Technology Standards (INCITS). Accordingly, the typical storage subsystem is robust in the sense that it can support a failure in one of its storage controllers and still provide speedy access to data of the various disk media.
One configuration of a storage subsystem is to arrange storage controllers as an active/passive array. Active/passive arrays allow I/O operations to take place over a primary storage controller. I/O or input/output is data transferred to or through a conductor or node. In this situation, the second storage controller is called a passive storage controller, while the primary storage controller carries I/O along an active path.
Occasionally, a hard disk drive may attempt to enter a quiesced state. The hard disk may attempt this state transition to respond to an error. However, the hard disk drive may attempt this state transition because of a change in ownership between the LUN to which the disk drive belongs and a storage controller. From a perspective of a prior art host, an active storage controller has failed, and the host is required to access LUNs through the passive storage controller. Accordingly, the prior art host would issue ownership change commands. Where multiple hosts rely on the same storage controller, the multiple hosts could issue ownership change commands that delay resumption of I/O from the hosts to their respective LUNs in the storage subsystem.
Consequently, a benefit may occur if such a delay could be reduced from that experienced by the prior art.